[jira] [Created] (ARROW-16254) [Python] Scalar constructors should be callable

["Antoine Pitrou (Jira)" <ji...@apache.org>]

Antoine Pitrou created ARROW-16254:
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             Summary: [Python] Scalar constructors should be callable
                 Key: ARROW-16254
                 URL: https://issues.apache.org/jira/browse/ARROW-16254
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Python
            Reporter: Antoine Pitrou
             Fix For: 9.0.0


Currently, to create a Scalar instance you must call the {{pa.scalar}} factory function. This works fine for the simplest types, but not for more elaborate ones.

For example, in C++ it is trivial to create a {{ListScalar}} from the embedded {{std::shared_ptr<Array>}}. But not in Python:
{code:python}
>>> arr = pa.array(["abc", "def", "ghi"])
>>> pa.ListScalar(arr)
Traceback (most recent call last):
  Input In [7] in <cell line: 1>
    pa.ListScalar(arr)
TypeError: __init__() takes exactly 0 positional arguments (1 given)
{code}

There is a clumsy workaround that creates an intermediate {{ListArray}} with trivial offsets:
{code:python}
>>> list_arr = pa.ListArray.from_arrays([0, len(arr)], arr)
>>> list_arr[0]
<pyarrow.ListScalar: ['abc', 'def', 'ghi']>
{code}




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